It sounds like they are making the claim that they can revoke access to data immediately, but they say you don't need to store the content on-device. I looked u

It sounds like they are making the claim that they can revoke access to data immediately, but they say you don't need to store the content on-device. I looked up "key displacement" and can't find any immediate references, though I'm not an expert. My understanding is that if I acquire a ciphertext encrypted with key v1, I will always be able to decrypt it. Any "asynchronous" protocol will have this problem, right? I can be revoked access if I need a piece of the key from a trusted party or if that v1 of the ciphertext can be guaranteed deleted, but caching old versions of keys and files means I will always retain access to the versions of files I ever had access to. Could someone with a bit more understanding shed some light on this?